Many vehicle manufacturers desire to reduce passenger compartment noise in motor vehicles to increase driver and passenger comfort. One source of noise that may enter the vehicle passenger compartment is engine noise generated or carried by the exhaust of the motor vehicle. Typically, the motor vehicle includes a muffler and tailpipe system to attenuate undesirable noises from the exhaust.
Another source of noise that enters the vehicle passenger compartment is engine noise broadcast by the air intake system of the vehicle engine. Because internal combustion engines comprise reciprocating pistons in cylinders that use valves to control air intake and exhaust, the air flow into the engine is not completely smooth but is pulsed. The pulsating nature of the air flow and other factors of engine design can cause shock waves in the air passages of the intake system that travel through the passages and are broadcast out of the intake duct creating additional noise making its way into the vehicle passenger compartment, for example, through the instrumentation panel.
Many techniques have been described in published literature detailing means to address the flow of noise out of the vehicle air intake to reduce engine generated noise. Such means include Helmholtz resonators, quarter wave length (side branch) ducts and even resilient ducts that are said to have noise attenuating properties. These solutions either provide only marginal improvement, have a limited operating spectrum or take up large amounts of valuable space in the vehicle engine compartment.